1. Field of Invention
The present invention relates generally to wireless charging technology.
2. Description of Related Art
Mobile terminals, such as a mobile phone, a Personal Digital Assistant (PDA) and the like, are driven with rechargeable batteries and the battery of the mobile terminal is charged through supplied electronic energy by using a separate charging apparatus. Typically, the charging apparatus and the battery have separate contact terminals at an exterior of each and are electrically connected with each other by contacting the contact terminals.
However, since the contact terminal outwardly protrudes in such a contact type charging scheme, the contact terminal is easily contaminated by foreign substances and thus battery charging is not correctly performed. Further, battery charging may also not be correctly performed in a case where the contact terminal is exposed to moisture.
Recently, a wireless charging or a non-contact charging technology has been developed and used for electronic devices to solve the above-mentioned problem.
Such a wireless charging technology employs wireless electric power transmission/reception, and corresponds to, for example, a system in which a battery can be automatically charged when a portable phone is not connected to a separate charging connector but instead, merely placed on a charging pad. The wireless charging technology is applied to a wireless electric toothbrush or a wireless electric razor and is well known to the public. Accordingly, a waterproof function can be improved since electronic products are wirelessly charged through the wireless charging technology, and the portability of electronic devices can be increased since there is no need to provide a wired charging apparatus. Technologies related to the wireless charging technology are expected to be significantly developed in the coming age of electric cars.
The wireless charging technology includes an electromagnetic induction scheme using a coil, a resonance scheme using a resonance, and an RF/microwave radiation scheme converting electrical energy to a microwave and then transmitting the microwave.
It is considered up to now that the electromagnetic induction scheme is mainstream, but it is expected that the day will come in the near future when all electronic products are wirelessly charged, anytime and anywhere, on the strength of recent successful experiments for wirelessly transmitting power to a destination spaced away by dozens of meters through the use of microwaves at home and abroad.
A power transmission method through the electromagnetic induction corresponds to a scheme of transmitting electric power between a first coil and a second coil. When a magnet is moved in a coil, induction current is generated. By using the induction current, a magnetic field is generated at a transmission side, and electric current is induced according to a change of the magnetic field so as to make energy at a reception side. The phenomenon is referred to as magnetic induction, and the electric power transmission method using magnetic induction has high energy transmission efficiency.
The resonance method was released as a coupled mode theory, and uses a concept of physics in which if a tuning fork is rung, a wine glass near the turning fork is also rung at the same frequency. Electromagnetic wave containing electrical energy have also been made to resonate instead of making sounds resonate. The resonated electrical energy is directly transferred only when there is a device having a resonance frequency and parts of electrical energy which are not used are reabsorbed into an electromagnetic field instead of being spread in the air, so that the electrical energy does not affect surrounding machines or people unlike other electromagnetic waves.
In the wireless charging system according to the conventional art, a wireless power transmitter is fixedly installed at a site while externally receiving electric power to transmit electric power, but not to receive electric power. In addition, the wireless power transmitter according to the conventional art cannot be carried by the user, and cannot transmit electric power without an external power source.